Can you attribute the apparent rise in autism rates and learning disabilities to environmental exposures?
Genetic, environmental, and social factors interact in complex ways to determine how the brain develops and functions. For autism, twin studies show that the concordance rates for identical twins varies from about 50% to 95% with a mean of approximately 75% in various studies. Interestingly, even in affected identical twins, the expression of neurobehavioral symptoms may vary considerably, suggesting that environmental factors influence genetic expression. In all likelihood, the syndrome of autism is actually a heterogeneous mixture of conditions with varying genetic and environmental contributions. Any true increases in the incidence of autism are almost certainly attributable primarily to environmental causes, and this is the subject of considerable research interest. Genetic, social, and environmental factors also play important roles in the origins of learning disabilities. Some neurodevelopmental toxicants unequivocally cause impairments of specific domains of learning. The extent
